In article ,
(Andy) wrote:

Schematic is here (warning, ~2mb file..)

http://www.hafler.com/techsupport/pd...20_amp_man.pdf

The instruction is given for the bias, but not for the balance.
How do I adjust the balance? Is this a good amp?

Thanks
Andy

It appears that the balance control adjusts the open loop slew rate
balance between positive and negative swings. A high frequency square
wave of moderate amplitude might help you. Adjust it so that that an
oscilloscope shows a symmetrical output waveform.

Or it might not work. Mark where the pot is before you turn it